Atomics WITHOUT C++11 support?

For backwards compatibility reasons, we need to support versions of C++ prior to C++11, so we cannot use std::atomic<...>. However, we still need atomics.

Is there an alternative to std::atomic<...> that's possible in previous versions of C++?

Preferably without including any new dependencies, but I realize this might be impossible.

EDIT: we need this specifically for Unix. We have considered Boost but don't want such a large dependency for one platform that we will upgrade to C++11 in a few years.